There is known an induction heater (RF Patent 2086759), including a housing, a body and three separate induction coils (one for each phase) with three radiators. The cavity between the housing and the body is filled up with transformer oil. The disadvantages of this heater are the design complexity, inefficient way of using of eddy currents in conversion of the electric energy into heat and, accordingly, high power consumption.
The closest related art (analogue) to the present invention is an induction heater (RF Patent 2284407), comprising a housing, a bearing element disposed coaxially with the housing with series-connected induction coils placed on it and provided with ferrite magnetic cores.
Furthermore, the bearing element is made in the form of a conductive nonmagnetic rod, to the bottom of which an out coming round wire of the lower coil is attached. The upper part of the bearing element is shorted to a logging cable armor shell via a connector; the primary winding of an upper coil is connected to a central core of the cable (CCC) via a connector. The upper part of the housing is made of non-magnetic non-electrically-conductive material; the lower part of the housing is made of magnetic electrically conductive material, wherein the coil windings are wound on ferrite magnetic cores of different diameters, and the upper coil windings are wound on a ferrite magnetic core of a larger diameter, and the lower coil windings are wound on a ferrite magnetic core of a smaller diameter. Disadvantages of this heater are large power losses when operating at great depths, for instance, from 5000 meters or more, as well as a low output frequency of about 1 kHz, which reduce efficiency of the heater.